Lab 23 A: Harmonic Motion

Purpose Harmonic motion is motion that repeats in cycles. Many important systems in nature and many useful inventions rely on harmonic motion. For example, the phases of the moon and the seasons are caused by Earth's harmonic motion. This Investigation will explore harmonic motion using a pendulum. The concepts you learn with the pendulum will also apply to other examples of harmonic motion.

Key Question How do we describe the back-and-forth motion of a pendulum?

Background Define: -Harmonic -Period -amplitude

Drawing Draw this:

Procedure Section 1: Start the pendulum swinging and watch it for a minute. Think about how to describe the motion.

Section 2: measure the period of your pendulum. Time ten cycles. Do three trials and use Table 1 to record your data. Divide the average time for ten cycles by 10 to get the period. Finish through this section by the end of the first day.

Section 3: 1. Attach the photogate as shown in the diagram. The pendulum breaks the light beam when it swings through the photogate. Try to keep the string length close to the length you used in part Put the Data Collector in period mode and let the pendulum swing through the light beam. 3. The reset (O) button does two things: If you press reset once the display freezes allowing you to write down a number before it changes. Pressing reset a second time starts another measurement.

Section 5: In this experiment, the period of the pendulum is the only dependent variable. There are three independent variables: 1) the mass of the bob, 2) the amplitude of the swing, and 3) the length of the string. 1.The amplitude can be changed by varying the angle that the pendulum swings. 2. There are washers that you can use to change the mass of the bob.

Section 5 cont: 3. The length of the string can be changed by sliding it through the slot in the peg. Measure the length of the string from the bottom of the string peg to the bottom of the washers. Design an experiment to determine which of the three variables has the largest effect on the period of the pendulum. Use DATA CHART!!!!! how many attempts per independent variable will be needed? Your experiment should provide enough data to show that one of the three variables has much more of an effect that the other two. Be sure to use a consistent technique that gives you consistent results.

Section 6: Split up your data so that you can look at the effect of each of the three variables by making a separate graph showing how each one affects the period. To make comparison easier, make sure all the graphs have the same scale on the y-axis (period).

Section 7: OMIT THIS SECTION

Post Lab: